Interactions between temperature and intercellular CO₂ concentration in controlling leaf isoprene emission rates

Area of Science:

• Plant physiology and atmospheric chemistry, focusing on biogenic volatile organic compound emissions.

Background:

• Plant isoprene emissions (I_s) influence atmospheric photochemistry.
• Previous studies suggest I_s decreases with increasing atmospheric CO₂, with temperature potentially modifying this response.

Purpose of the Study:

• To investigate the interactive effects of intercellular CO₂ concentration (C_i) and temperature on isoprene emission rates (I_s) in hybrid poplar trees.
• To understand the drivers of seasonal variations in I_s, particularly midsummer downregulation, in a warm climate.

Main Methods:

• Field measurements of isoprene emission rates (I_s) in hybrid poplar trees.
• Analysis of the relationship between I_s, intercellular CO₂ concentration (C_i), and temperature throughout the growing season.
• Interpretation of results in the context of regional weather patterns and plant metabolic processes.

Main Results:

• An unexpected midsummer downregulation of I_s was observed, despite high temperatures.
• High temperatures suppressed the I_s:C_i relationship throughout the growing season.
• The sensitivity of I_s to increased C_i was highest during the midsummer period when I_s was lowest.

Conclusions:

• Seasonal downregulation of I_s and increased sensitivity to C_i are linked to monsoon weather system onset.
• Temperature suppression of the I_s:C_i relationship is explained by chloroplastic inorganic phosphate dynamics and metabolic fluxes affecting phosphoenolpyruvate import.